Preventing the caking of sodium perborate



Patented Oct. 15, 1940 3:.

I This invent-ion relates to the preparation oi v PEBBOBATEQ. v

Joseph SJReichertand Allen M; Taber, Niagara Falls, N; 'Y., Vassignors to'E. :I. du Pontde Nemcurs & Company, Wilmington, Del;,,a1-corporation of Delaware No Drawing.

A plic tion-September 29; 1937', Serial No. 166,395

anti-caking mixtures'of powdery materials. More particularly, it relates to'the preparation of anti-- I caking preparations of sodium perborate.

Sodium perborate, usually sold in commerce in the form of the tetrahydrate, NaBOaAI-IzO, is a fine powdery material which has a decided tendency to cake during storage. Wherever the powder is subjected to conditions of relatively high humidity, such as during storage in warm climates or during thesummer season, the powder cakes to a degree which seriously interferes with its'utilization. Since sodium perborate is largely used in oral and dental preparations it is essential that it remain free flowing under 'substan tially all conditions of use. 'Caking and hardening during storage, possibly accompanied to some extent by loss of water, is detrimental and ren- V be rendered free flowing under practically all conders less satisfactory the ordinary sodium borate. of commerce. p

We have now found that sodium perborate, particularly the tetrahydrate, NaBO3.4I-I2O, may

ditions of storage if there is incorporated with the perborate a small amount magnesium oxide (MgO) We have found, however, that it is necessary to employ magnesium oxide of relatively low bulk density as satisfactory anti-caking action is not obtainedwhen the density of the magnesium oxide exceeds about 450 grams per liter of volume. Preferably we utilize the relatively lighter grades of magnesium oxide,'suchvas those having a bulk I density of 120 grams per liter or less. Magnesium oxide of the grades having bulk densities ranging from 120 grams per liter to 450 grams per liter is termed light magnesium oxide throughout the remainder of the specification and claims.

Amounts of light magnesium oxide ranging from 4 to 10%, based upon the weight of the sodium perborate stabilized against caking, have been found most suitable. It may be stated that the reduction in the tendency of the sodium perborate to cake is more or less directly proportional to the amount of magnesium oxide oflight bulk density" added. However," we have found that amounts, of light magnesium oxide in excess of 10%,while tending to increase the free flowing characteristics of the sodium perborate to a certain extent, do not add sufficiently to the anticaking tendencies of the powder to warrant the employment of amounts of magnesium oxide of light grade eater than that percentage.

While the use of magnesium hydroxide as an anti-caking agentfor sodiumperborate has been disclosed in the patent literature, we have found was divided into two equal portions.

amount of 6%, based upon the weight ofthe per- 1 sodium perborate, was added. Thevmagnesium mately two weeks.

. pared with a sample of untreated sodium perthatmag'nesium oxide of the previously specified light bulk density is very much more satisfactory than the hydroxide. We have observed that light magnesium oxide is at least five times more effective than magnesium hydroxide in eliminating the tendency of the sodium perborate to cake when equal amounts of each agent up to 10% by weight, based upon the weight of the sodium perborate stabilized, are present. I

As illustrative of our novel sodium perborate stabilized against caking by the addition of magnesium oxide of light bulk density the following examples may be given:

Example 1 e A sample of sodium'perborate inpowder form v To-one of these portions -magnesium hydroxide in the hydroxide was thoroughly and evenly dispersed throughout the perborate by thorough stirring.

' To the other portion a light grade of magnesium oxide having a bulk density of about 120 grams per liter was added in the amount. of 6% by a weight based upon the weight of the sodium perborate. The light magnesium oxide was also I thoroughly and evenly dispersed throughout'the perborate by thorough mixing. I

The free flowing properties of each powdery O product were then compared by visual observation. Previous to the comparison the samples were stored in a moist atmosphere for" approxi- It was observed that the sodium perborate powder containing light magnesium' oxide as the anti-caking agent had ap-, proximately one-fifth ofthe tendency to cake that the sample of sodium perborate containing the magnesium hydroxide possessed. When comborate, it was found that the sodium perborate sample stabilized against caking by the addition of light magnesiumoxide was approximately25 times as free flowing as the untreated sodium perborate tetrahydrate. 1

Example? Two samples of sodium perborate tetrahydrate were prepared. To one of these samples was added approximately 4% of magnesium hydroxide which was thoroughly and evenly dispersed5 throughout the mass bythoroughmixing. To the other sample was added approximately 4% of a light grade of magnesium oxide having a bulk density of approximately 447 gramsper liter.

This sample was also thoroughly agitated to ,se-

two weeks. The powdery product containing the light magnesium oxide as an anti-caking, agent had approximately one-half the tendency to cake that the other sample. of sodium perborate, that containing the magnesium hydroxide, possessed. When compared with untreated and unstabilized sodium perborate powder, it was observed that the sample containing light magnesium oxide had approximately one-tenth the tendency to cake upon storage that the unstabilized sample had.

It is to be understood that the foregoing examples are merely illustrative and by no means limit the scope of our invention. Our invention may be incorporated in various otherv embodidered form and magnesium oxide of bulk density ranging from 120 grams per litre to 450 grams per litre, said magnesium oxide being present in amounts ranging from 4 to 10% by weight based on the weight of said perborate.

2. A dry mixture of sodium perborate in powdered form and magnesium oxide of bulk density not exceeding 450 grams per liter, said magnesium oxide being present in amounts ranging from 4 to 10% by weight based on the weight of the sodium perborate.

JOSEPH S. REICHER'I'. ALLEN M. TABER. 

